As per Ooma support, I found some troubleshooting steps you may try with the step below :

First start by checking your internet hardware. Make sure your modem lights display you have internet connectivity.
You may need to contact with your ISP.

Next check the lights on the Ooma device.

If you have the Ooma Hub, check the tab in the upper left-hand corner of the device. The light should be Blue
If you have the Ooma Telo, check the logo in the center of the Telo device. The light should also be Blue.
If the light is not blue, please refer to the Quick Start Guide to make sure your Ooma is connected correctly.